The principal objective of this proposal is to determine how visual interneurons interact to detect movement and directions of movement. Intracellular recordings will be made in the turtle retina from directionally selective (DS) ganglion cells and from recently discovered DS amacrine and bipolar cells, and in the fly optic lobes from 3d and higher order, movement detecting neurons and their photoreceptor, laminar, and medullary cell inputs. Identifications of penetrated cells will be made by intracellular injections of Lucifer yellow, and it will be seen if there are any dye couplings between similar or dissimilar cells. The principal stimuli will be moving gratings. To understand the underlying mechanisms of motion detection better, the periodic responses elicited by these sequential stimuli will be compared, using Fourier analysis, with flicker responses to simultaneous periodic stimuli. In the turtle retina, the main questions to be answered are whether or not directional selectivities result from interactions within a network of DS ganglion, amacrine and bipolar cells and what the roles of GABAergie and cholinergic amacrine cells are. Secondarily, spectral sensitivities of horizontal cells will be measured in order to confirm the identities of R/G and B/G color opponent cells, to characterize the spectral properties of H4, and to test models of inputs onto horizontal cells of cones with known action spectra. Spectral sensitivities of other, DS and non-DS cells will also be measured. In the fly optic lobes, small-field DS cells of the medulla (the elementary motion detectors) will be identified, and they will be characterized physiologically. The transmission of sequential vs. simultaneous periodic information from the photoreceptors to the small-field DS cells will be analyzed stage by stage using harmonic analysis of waveforms and pharmacological agents to modify these waveforms. The possible inhibitory roles of large-field, non-DS medullary cells in nonlinear areal summation of lobular plate giants will be tested.